1. Field of the Invention
The present invention relates to an aqueous coating agent for forming lubricating films, in particular, to an aqueous coating agent for forming lubricating films suitable for prolonged use on sliding members of torque-transmitting parts utilized in automobile drive and prime mover systems.
2. Description of the Related Art
Conventional aqueous coating agents for forming lubricating films, in particular those for use with sliding parts, comprise substances which possess excellent oil-proof and heat-resistant properties and are formed by dispersing molybdenum disulfide, graphite powder or carbon fibers in binders such as a polyimide resin, an epoxy resin, or a phenol resin.
Although aforementioned coating agents for forming lubricating films in an aqueous-system form are known as well, in the majority of cases such coating agents are based on organic solvents. For example, in their earlier patent application (Japanese Laid-Open Patent Application Kokai 6-200275) the authors of the present patent application utilize an organic solvent.
Recently, however, more strict requirements were imposed concerning environment protection and reducing the impact on human health. For this reason, many industries had to quickly switch from organic solvent systems to aqueous systems.
For the same reason, there is a strong demand for aqueous systems exists also in the field of coating agents for forming lubricating films. An example of such a water-based coating agent for forming lubricating films is disclosed in Japanese Laid-Open Patent Application Kokai 7-11088 wherein silica is used as an agent for imparting lubricating properties. However, this aqueous coating agent for forming lubricating films appears to be unsuitable for prolonged use on sliding members of torque-transmitting parts utilized in automobile drive and prime mover systems.
The present invention is aimed at elimination of the problems of the prior art, and it is an object of the present invention to provide an aqueous coating agent for forming lubricating films with improved lubricating properties, long-service life, in particular, on sliding members of torque-transmitting parts utilized in automobile drive and prime mover systems, and excellent load-bearing properties.
The present invention is characterized by the fact that, in an aqueous coating agent for forming lubricating films, a number of specific solid lubricating agents is used in a specific weight ratio range, and that the aforementioned solid lubricating agents is used in a specific weight ratio with regard to a hydrophilic resin.
In other words, the problems inherent in the prior art are solved by utilizing an aqueous coating agent for forming lubricating films that comprises the following first component, second component, and third component: the first component: a hydrophilic resin; the second component: a solid lubricating agent comprising MoS2 and at least one antimony sulfide selected from the group consisting of Sb2S3 and Sb2S5, where the weight ratio of MoS2 to antimony sulfide is from 1:0.05 to 1:1.2; and the third component is water. The weight ratio of the second component to the first component is from 0.7 to 3.